Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$197.66	6.438%	$210.3854	$210.39	$210.40	$210.40
Purchase #2	$102.94	7.860%	$111.0311	$111.03	$111.05	$111.00
Purchase #3	$85.46	8.414%	$92.6506	$92.65	$92.65	$92.70
Purchase #4	$35.82	5.382%	$37.7478	$37.75	$37.75	$37.70
Purchase #5	$195.87	7.696%	$210.9442	$210.94	$210.95	$210.90
Purchase #6	$66.67	7.367%	$71.5816	$71.58	$71.60	$71.60
Purchase #7	$56.93	11.512%	$63.4838	$63.48	$63.50	$63.50
7 purchase totals =	$741.35		$797.8245	$797.82	$797.90	$797.80